Etching



Feb. 23, 1960 w. GUENST 2,926,076

ETCHING Filed May 14, 1957 2 Sheets-Sheet 1 6. P1102 A rf W. GUENST Feb. 23, 196@ ETCHING 2 Sheets-Sheet 2 Filed May 14, 195'? lNvENToR zzam Gaze/rst E'rcnlNG Gnenst, Elkins Park, Pa., ass'ignor to Master Etching Machine Company, Wyncote, Pa., a corporation of Pennsylvania y Application May r4, 1951, serial No. 659,168

` s claim.' (ci. 414z) The present invention relates to etching machines and processes of etching, particularly applicable to etching using etchants` which are elective primarily on direct impingement.

The present application is a continuation-in-part of my copending application Serial No. 596,190, iiled July 6, 1956, for Etching, now abandoned. i `A purpose of the invention is to obtain more effective etching on the relief surfaces of a printing plate, especial-l ly of cylindrical form, while'avoiding undercutting. A further purpose is to avoid improper distribution of retardant on' portions of the printing'plate which are undergoing spraying of etchant and to avoid air hardening of retardant on the surface. l f A further purpose is to avoid nonuniform etching on a printing plate, especially a cylindrical printing plate, by virtue of the differencein etching between a surface which is rising toward a source of liquid ow and a surface which is descending withlthe liquid flow; for

2,926,076 y Patentedreb, 23, leso Y 2 section of a printing plate showing the eiect of etching in the prior art.

Figure 7 is a view similar to Figure 6, showing the eiect-of etching according to the invention.

Figure 8 is a diagrammatic central vertical section of Y a modied embodiment of the invention.

Describing in illustration but not in limitationl and referringto the drawings:

In the prior art, diiculty has been encountered in etching printing plates uniformly. Nonuniformity of etching has'occurred and a specialized type of nonuniform etching known as undercutting has been a prob'- lem. Thus, as shown in Figure 6, a printing plate A having a dot 2.1 has a dot facing 22. The plate proper isetched'away at 23 but also the side of the dot becomes undercut by the etchant at 24, weakening the dot structure or destroying it completely. This diiiiculty occurs `in etching with nitric acid and numerous other etchants.

To overcome this diiculty, improved etching techf niques have been developed, in some cases introducing p retardants which tend to make etching more uniform and example, to avoid the diierence in etching eect between the ascending side of a rotating cylinder and they descending side of the cylinder, where spray is beingapplied 'at the top'with the cylinder axis horizontal.

A further purpose is to l'substantially completely, or completely, Vsubmergethe plate in an etchant bath, spray etchant-at one part of the plate, and manipulate the plate to expose successive parts to the spray, the immersion orl partial immersion of the plate in the bath protecting against nonuniform etching and against hardening of the retardant.

A further` purpose is to regulate the ilow through the spray.

i A further purpose is to draw etchant to be'sprayed simultaneously from both the upper and lower parts of the bath, and preferably to regulate rthe ratio between the quantity drawn from the upper portion and thev quantity drawn from the lower portion. f

Furtherpurposes appear in the specification and in the claims.

In the drawings I have chosen -to illustrate a few only of the numerous Aembodiments in which the invention may appear, selecting the forms Yshown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved. Figure` 1 is a fragmentary diagrammatic top plan view of an etching machine according to the invention.

Figure 2 is a section'on the line 2 2 of Figure l. fr' Figure 3A is a diagrammatic end elevation, highly exaggerated, showing the edge of a cylindrical plate in the prior art.

Figure 4 is a view similar to Figure 3, showing the etching in accordance with one embodiment of the invention.

Figure 5 is a view similar to Figure 3 showing the etching according to another embodiment of the invention.

Figure 6 is an enlarged and exaggerated transverse reduce undercutting. While the principles of the invention are applicable to all types of printing plates, whether the metal used is copper base alloy, aluminum base alloy, magnesium base alloy or otherwise, it will be suicient to refer to the protective techniques described in Easley and Swayze U.S. Patents Nos. 2,640,763 to 2,640,767, granted June y2., v1953, for Etching. These patents relate particularly to plates of magnesium, zinc and theiralloys.

According to the etching techniques above referred to, the etchant is primarily effective on direct spray impingement, and is not substantially effective on lateral contact.v

Thus as shown in Figure 7, a printing plate 20 receiving spray indicated by arrows 25 is etched at 23 in the area Ibetween dots 22, but the side of the dot at 24 is protected andl is not undercut. The protection at 24 is accomplished by a lul of retardant 26', which is removed by direct impingement of the spray at 23, but is not removed by lateral contact at 24. 'I'he particular re-, tardant used may, for example, be diethylbenzenewetting agent, having the property of forming `a lm on the plate, and separatingfrom the etchant solution, usually nitric acid solution, by reason of the lighter speciic gravity of the retardant.

i Efforts have been made to apply spray to a printing plate,such as cylindrical printing plate, in such a way plate.

as to obtain the etching eiect indicated in the theoretical discussion in reference to Figure 7. Thus, as shown in Figure 3, a cylindrical plate 202 has been mounted on a horizontal axis 27 and rotated in air in the direction of the arrow 28 While being sprayed across the top by jets 25, using an etchant and a retardant. The results obtained under these conditions have been very unsatisfactory. The etchant and retardant ow down both sides at 30 and 31l and drop ofr the bottom at 32. On the side having the flow 30, however, the downward ow of the` etchant and retardant is opposite to the upward motion of the side of the plate as it rotates, while on the side having the'flow 31 the downward flow is in the same direction as the motion of the side of the printing has tended to form a hardened deposit due to the long air exposure, so that it was diiiicult for the direct spray to remove the lm and accomplish etching.

I have discovered that this difficulty can be overcome by placing the printing plate on its side and manipulating it partially or wholly submerged under the etchant bath. The bath surrounding the plate tends to carry away the etchant flow as soon as the spray meets the bath and when the plate is completely submerged beneath the bath it tends to soften or mitigate the etching and prevent hardening On the side having the flow 30 there has been. relatively nonuniform etching. Also the retardant hlm,

of the retardant film. As shown in Figure 4, the plate 202 is wholly immersed in the etchant bath 33, and the spray 25 strikes the top of the rotating plate through a fraction of an inch or a few inches of etchantbath. Thus, though the spray is forcefully impinged'to break the retardant film and accomplish etching on direct impingement at points where etching is to be accomplished, there is no difficulty through irregular etchant action beneath the bath, nor is trouble caused by hardening of the protective film.

Figure shows a modification in which the level 34 of the bath is just below the portion of the rotating cylindrical plate which is being sprayed. Here again the bath prevents nonuniformity of etching and protects against undue hardening of the film. Only the portion of the plate adjoining the spray is exposed to the air.

The etching machine illustrated in Figures 1 and 2 comprises a base 35 supporting an etchant tank 36 suitably of rectangular form. The one end of the etchant tank mounts a combined stuffing box and bearing 37 which supports a horizontal rotating shaft 38 driven by motor pulley 40 and belt 41 to pulley 42 on the end of shaft 38 outside the tank.

Suitably mounted on the horizontal shaft axis is a plate holder 43 which supports a cylindrical printing plate 44 being rotated by the shaft. Space is provided at one end of the tank to remove the plate to the position 44' from which it can be lifted out of the tank.

The tank is covered in any suitable lway not shown.

Mounted at one side of the tank is a vertical outlet tube 45 in a vertical sliding guide 46 on the tank. The tube has a supporting rod 47, which passes up through opening 48 in retainer bracket 50 on the tank wall and is held in any suitable position by set screw 51. The tube has an inlet opening near the top at 52 in the area 53 of the bath 33 which will predominantly contain lighter retarding agent. The tube 45 terminates at the bottom, leaving a clearance 54 from the bottom so as to permit withdrawal also of the predominantly heavy etchant 55. It will be evident that by moving the tube up or down less or more of the retardant compared to the etchant will be Withdrawn by the pump. In line with the tube is a U bend outlet pipe 56 which communicates at the bottom with a pump chamber 57 containing pump rotor 58 which turns on shaft 61 on bearing 60, and turning in housing 62 under the action of motor 63.

Tangential to the pump housing is a pump outlet pipe 64 which extends upward at 65 and across the top of the etching machine at 66 and then down at 67 to a header 68. The header mounts and connects with spray pipes 70 extending along horizontally above and close -to the cylindrical printing plate and the pipes have spray openings 71 at their lower sides directed downwardly and radially of the cylindrical plate. The spray pipes are closed by caps 72 at the far ends.

For the purpose of regulating the ow through the sprays, a branch pipe 73 connected to pipe 66 communicates with a by-pass valve 74 which discharges through a by-pass pipe 75 back into the bath.

In operation, the printing plate is secured in any suitable way on the drum 43 with its outer surface partially or preferably wholly immersed in the etchant bath. If the plate is not to be Wholly immersed, it Should be immersed to about the outer contines of the spray. The tube 45 is then adjusted by moving it up or down to obtain the proper proportion of etchant and retardant in the spray. The pump 58 is then operated and the by-pass valve 74 is opened or closed to obtain the desired flow through the spray nozzles.

The etching then continues, the spray clearing away the retardant film on direct mpingement and thus etching areas 23, but the retardant protecting the sides of the dots against undercutting and also protecting against etching while the plate is removed from the spray and is travelling beneath the bath.

Thus in effect the spray selectively etches the parts which are not protected by the resist or other means applied in the etching process, and are not subjected to the direct impingement In some cases, the spray may be obtained from an impeller or impellers rather than a spray head. In Figure 8 I illustrate a plate holder and plate mounted and manipulated in the manner previously described, in a well 76 of a tank 77 which is provided with etching spray impellers 78 driven by shafts 80 through motors 81 and belt and pulley combinations 82. Impellers are backed up by a spray directing shields 83, andthe spray is confined by direction vanes 84. The plate may be submerged to any of the extents referred to. While in this case spray is directed on the plate from both sides, it will be understood that in a suitable design the spray can be received from only one side if desired.

The plate is removed by opening a. cover 85.

In view of my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art to obtain all or part of the beneits of my invention without copying the method and structure shown, and I, therefore, claim all such insofar as they fall the reasonable spirit and scope of my claims.

Having thus described my invention, what I claim. as new and desire to secure by Letters Patent is:

1. The method of etching a cylindrical printing plate, using a chemical etchant which is effective primarily on direct impingement, which comprises maintaining a pool of etchant, immersing the cylinder at least partially bcneath the pool with a portion of the cylindrical surface upwardly exposed, directing a spray of etchant on the upwardly exposed surface of the cylinder, and rotating the cylinder.

2. The method of claim 1, which comprises maintaining the cylinder fully immersed in the pool.

3. The method of etching a cylindrical printing plate using a chemical which is elective principally on direct impingement, and which includes ingredients of different specific gravity, which comprises maintaining a pool of the etchant, at least partially immersing a printing plate beneath the pool of etchant, withdrawing liquid from the pool at both the lower and upper portion of the pool, spraying the liquid withdrawn against a portion of the printing plate and rotating .the cylinder to expose successive portions of the circumference of the cylinder to the spray.

References Cited in the file of this patent UNITED STATES PATENTS 519,595 Thofehrn May 8, 1894 1,188,870 Williamson June 27, 1916 2,074,221 Holland Mar. 16, 1937 2,155,392 Ballard Apr. 25, 1939 2,307,928 Hogaboom Ian. 12, 1943 

1. THE METHOD OF ETCHING A CYLINDRICAL PRINTING PLATE, USING A CHEMICAL ETCHANT WHICH IS EFFECTIVE PRIMARILY ON DIRECT IMPINGEMENT, WHICH COMPRISES MAINTAINING A POOL OF ETCHANT, IMMERSING THE CYLINDER AT LEAST PARTIALLY BENEATH THE POOL WITH A PORTION OF THE CYLINDRICAL SURFACE UPWARDLY EXPOSED, DIRECTING A SPRAY OF ETCHANT ON THE UPWARDLY EXPOSED SURFACE OF THE CYLINDER, AND ROTATING THE CYLINDER. 